1. Technical Field
The present invention relates to a photoconductive antenna, a camera, an imaging device, and a measurement device.
2. Related Art
In recent years, terahertz waves which are electromagnetic waves having a frequency equal to or greater than 100 GHz and equal to or less than 30 THz have attracted attention. The terahertz waves can be used in, for example, various types of measurement such as imaging and spectroscopic measurement, non-destructive tests, and the like.
Terahertz wave generation devices that generate such terahertz waves include, for example, a light pulse generation device that generates a light pulse having a pulse width of approximately subpicoseconds (several hundred femtoseconds), and a photoconductive antenna that generates a terahertz wave by irradiation with the light pulse generated in the light pulse generation device.
For example, JP-A-2009-124437 discloses a photoconductive antenna including a semi-insulating GaAs substrate, a GaAs (LT-GaAs) layer formed on the semi-insulating GaAs substrate by a low-temperature MBE (molecular beam epitaxy) method, and a pair of electrodes formed on the LT-GaAs layer. Further, JP-A-2009-124437 discloses that free carriers excited in the LT-GaAs layer are accelerated by an electric field caused by a bias voltage, whereby a current flows, and a terahertz wave is generated due to a change in this current.
The intensity of the terahertz wave which is generated in the above-mentioned photoconductive antenna is preferably large, whereby it is possible to realize a camera, an imaging device, and a measurement device having, for example, high detection sensitivity.
It is known that the intensity of a terahertz wave which is generated in a photoconductive antenna is dependent on the carrier mobility of a layer through which carriers transfer (travel) in the photoconductive antenna. That is, as the carrier mobility of the layer becomes larger, the intensity of the terahertz wave which is generated in the photoconductive antenna becomes larger.
In the photoconductive antenna disclosed in JP-A-2009-124437, since the carrier mobility (electron mobility) of the LT-GaAs layer has a small rate of 100 cm2/Vs to 150 cm2/Vs, the time variation of a photocurrent decreases, and thus it may not be possible to generate a terahertz wave having a large intensity. For this reason, it may not be possible to realize a camera, an imaging device, and a measurement device which have high detection sensitivity.